Method of orienting a speaker magnet



p 1970 R. J. PARKER METHOD OF ORIENTING A SPEAKER MAGNET Original FiledDec. 21, 1965 FIG.3

//VVENTOR 24 28 25 FIG. 4 Z7 2s .30 1 ROLLIN J.PARKER ATTORNEY UnitedStates Patent US. Cl. 148-103 2 Claims ABSTRACT OF THE DISCLOSUREPermanent magnets are oriented so as to have a preferred direction ofmagnetization along a curved path disposed about the axis of the magnet,with a first pole around a first portion of the side surface of themagnet and a second pole around an axially spaced second portion of theside surface of the magnet. The process comprises raising the magnet toa temperature above its Curie temperature, surrounding the magnet with amagnetic field axially aligned with the permanent magnet, and passingthe magnetic field axially through the permanent magnet from one of saidpoles to the other of said poles, while the magnet is cooled through itsCurie temperature.

This is a division of application S.N. 515,401, filed Dec. 21, 1965, nowUS. Pat. 3,440,364.

This invention relates to permanent magnets and permanent magnetassemblies for use in speakers and to a process and apparatus for theproduction of such magnets and magnet assemblies.

Permanent magnets ordinarily used in permanent magnet speakers areanisotropic, i.e., they are oriented along a preferred direction ofmagnetization. This is accomplished by subjecting the permanent magnets,during cooling of the magnet in its magnetic hardening process, to amagnetic field coinciding with the preferred direction of magnetization.Such method of orientation is disclosed, for example, in Jonas US. Pat.2,295,082.

Typical permanent magnet speakers contain a permanent magnet, a polepiece and one or more return path elements, all arranged in magneticcircuit relationship. The magnetic flux in such circuits flows axiallythrough the magnet, turns 90, and flows radially across an air gap tointeract with a voice coil. Thus the path of the magnetic circuit isgenerally rectangular. To enhance the performance of such speakers, themagnets are oriented along a preferred direction of magnetization whichruns axially through the magnet to coincide with the path of themagnetic circuit. The structure of permanent magnet assemblies inloudspeakers is, to a large extent, dependent upon and determined by thepath of the magnetic circuit in such permanent magnet assemblies, whichin turn is closely interrelated with the preferred direction ofmagnetization or orientation of the speaker magnet.

It is a principal object of the present invention to provide a speakermagnet which is oriented along a path which permits substantialimprovements in the design of permanent magnet circuits used inloudspeakers.

It is an additional object of this invention to provide a permanentmagnet assembly for use in loudspeakers which is simpler, has fewerparts and nevertheless possesses greater magnet efficiency thanpresently known magnet assemblies.

The objects of this invention are generally achieved by the provision ofa permanent magnet having a principal or preferred direction ofmagnetization lying along an axially disposed curved path, the open endsof which intersect the side surface of the magnet. In effect, themagnetic flux flows out the sides of the permanent magnet rather thanthe ends. The result is a higher efficiency speaker Patented Sept. 1,1970 magnet because the flux is concentrated where it should be-in theair gap. A second result is that the magnetic circuit in a speakercomprising the permanent magnet and the return path elements isconsiderably simplified. No bottom return path element or top pole pieceis necessary and it is possible, as set out more fully below, tosimplify and make more compact even those elements of the return pathwhich remain. Yet another aspect of the invention involves a uniquemethod for orienting the permanent magnets in the manner described.

The invention will be more clearly understood from the followingdescription taken in connection with the accompanying drawing in which:

FIG. 1 is an elevational sectional view of a cylindrical speaker magnetof the invention showing the manner of its orientation;

FIG. 2 is a sectional view of a permanent magnet assembly of theinvention comprising a return path element and a permanent magnet;

FIG. 3 is a sectional view of a speaker embodying the permanent magnetassembly of the invention; and

FIG. 4 is a sectional view of an apparatus suitable for orientingpermanent magnets in accordance with the invention.

As can be seen in FIG. 1, a cylindrical speaker magnet 1 having endsurfaces 2 and 3 at opposite axial extremities and a side surface 4 isoriented so that its preferred direction of magnetization is along acurved or arcuate path 5 disposed symmetrically around the central axisAA of the permanent magnet. It will be noted from FIG. 1 that the curvedpath 5 intersects with side surface 4 of the magnet at 6 along the topportion of the magnet and at 7 along the bottom portion of the magnet.Thus, a first pole will be created along one extremity of a side surfaceof the magnet at 6 and a second pole will be created on the oppositeextremity of the side surface of the magnet at 7. The path of preferredmagnetization shown in section in FIG. 1 extends symmetricallycompletely about the axis of the permanent magnet. The path oforientation is therefore described by rotating curve 5 through acomplete 360 are about the central axis AA of the magnet. Any planepassing through the central axis of the magnet would produce theorientation path shown in section in FIG. 1.

The utilization of a permanent magnet in a speaker magnet circuit,oriented as shown in FIG. 1, is shown in FIG. 2. As there illustrated,all that is necessary to complete the magnetic circuit is an opencylindrically shaped return path element 8. The permanent magnet 1 fitswithin and is coaxial with return path element 8. A flange 9 on theinner surface of return path element 8 contacts the permanent magnet 1along its lower extremity 7. The opposite extremity 6 of the sidesurface of the permanent magnet is spaced from return path element 8 toform the air gap 10.

The permanent magnet-return path structure shown in FIG. 2 permits anumber of significant advantages in the construction of permanent magnetspeakers. Measurements indicate that of the total magnetomotive force ismade available at air gap 10 as opposed to 65% to 75% in conventionalmagnet structures. Additionally, virtually of the total magnetic fluxmay be made to enter the general region of the voice coil versus a lossof as much as 20% of such flux to regions outside the voice coil regionin conventional magnet structures. In substance, use of a magnetoriented as illustrated in FIG. 1, with the return path assemblyillustrated in FIG. 2, makes possible the utilization in speakerstructures of a much higher percentage of the energy of conventionalpermanent magnets.

The invention also makes possible the utilization of return pathelements of thin-gauge metal. This is possible because the greaterefficiency of the magnetic circuit permits the use of lower fluxdensities to achieve an equivalent air gap density and thus equivalentspeaker performance. A conventional return path or yoke structure in aspeaker must have sufficient cross-sectional area so that the fluxdensity does not exceed the saturation point of the metal. Because theflux density per unit area of return path is smaller in the speakerstructure of this invention, less cross-sectional area in the returnpath element is necessary. This enables efficient speaker magnetstructures to be built utilizing thin-gauge, soft-steel return paths. Anadditional reason why the return path elements of the invention need beof less cross-sectional area is based upon the fact that the magneticflux is distributed over a wider area at the point of contact with thereturn path element.

The foregoing is illustrated more clearly in the speaker shown in FIG. 3of the drawing. Speaker basket 11 has depended from its central portiona tubular return path element 12 integral with and formed from thespeaker basket. It is possible to use metal from the speaker basket,previously discarded in the stamping of such baskets, to make the returnpath elements of the speaker both because of the simplified design ofthe return path and because of the ability to use lighter gauge metal.This aspect of the invention is more fully disclosed in my copendingapplication Ser. No. 515,322 filed Dec. 21, 1965, now U.S. Pat.3,466,405 and assigned to the same assignee as the present application.The remaining components of the speaker are a frusto-conical diaphragm13 and a flexible spider 14. A voice coil 15 is Wound on a voice coilform 17 and is coupled to diaphragm 13.

Another advantage of the invention is also illustrated by FIG. 2. Thewidth of the air gap is the same as the Width of the throat 17 formedbetween the remainder of the return path element and the lateral sidesof the permanent magnet. While this structure is not unknown in thespeaker art, it has almost always been avoided because greatestefficiency in speaker structures is obtained by maintaining a largedegree of separation between the axial flow of magnetic flux in themagnet and the return axial flow in the lateral portion of the returnpath. This discourages radiation of flux from the sides of the magnet tothe return path element at areas other than the air gap. In conventionalspeaker assemblies the flux flows in an axial direction through thepermnent magnet-any radial flow of flux other than at the extremities ofthe magnet must be discouraged. In the seaker magnet assemblyconstruction shown in FIG. 2, there is already a radial component(toward the sides of the magnet) in the flow of flux in the magnet 1 sothat radial flow is not discouraged except for a very small area at theaxial center of the magnet. It is thus possible to reduce considerablythe dimensions of the throat area of the permanent magnet return pathsystem and in turn to miniaturize the construction of the speaker. Whilethe invention does not require in all cases that the air gap and throatwidth be the same dimension (as in FIGS. 2 and 3), the inventionnevertheless does make it possible for the throat section to be narrowerthan in conventional speaker structures.

The present invention also encompasses a unique method for orientingmagnets along the direction set forth in connection with the descriptionof FIG. 1 above. An apparatus suitable for so orienting the permanentmagnets of the invention is shown in FIG. 4. Such appa ratus includes aceramic tube 19 containing the permanent magnets 20, 21, 22 and 23. Softiron washers 24, 25, 26 and 27 at the juncture of each two permanentmagnets act as pole pieces. An outer cylindrical tube 28 of anymagnetically permeable material, such as soft iron, surrounds the entirestructure and acts as a return path element. The outer tube 28 is woundin periodic fashion by windings 29, 30, 31 and 32 to create a series ofpoles of opposite polarity at the extremities of the magnets. Thus, itis wound in a first direction around magnet 20,

an opposite direction around magnet 21, the first direc tion aroundmagnet 22, and so forth, to create alternating north and south polessurrounding abutting end portions of the permanent magnets. As can beseen in FIG. 4, this arrangement permits magnetic flux to flow fromwashers 24, 25, 26 and 27 through an arcuate or curved path in each ofthe cylindrical magnets to an opposite pole at the next successivewasher, through the return path element to repeat the circuit. Thiscircuit is illustrated in the drawings for three of the magnets butwould of course be repeated throughout the orientation device.

By arranging any number of such periodic fields around a thermallyinsulating, temperature-resistant tube such as tube 19 containing thespeaker magnets, a number of such speaker magnets may be oriented inaccordance With the teachings of this invention. The permanent magnetsare first heated to a temperature above their Curie temperature, andpreferably about 300 C. above their Curie temperature, and then cooledthrough the Curie temperature to room temperature in accordance with aprescribed cooling cycle, while the magnets are subjected to a magneticfield in the foregoing apparatus. The cooled magnet will be orientedalong the curved path described above.

A specific example of the process of the invention is as follows:

Ceramic tube 19 (FIG. 4) is loaded with a plurality (as, for example, ahundred) sand-cast cylindrical alnico 5 permanent magnets ground toproper dimensions and having the following composition in percentages byweight: 8 aluminum, 14 nickel, 24 cobalt, 3 copper, balance iron. Thetube is placed in an induction heater and the tube and magnets areheated to 1100 C. The Curie temperature of the alnico 5 composition isabout 800850 C. The tube and magnets are then removed from the inductionheater and placed in the magnetic field orientation device illustratedin FIG. 4. Each magnet is aligned such that the line of contact betweentwo adjacent magnets falls centrally within one of the washers 24, 25,26 and 27. The permanent magnets are then allowed to remain in theorientation field while the periodically arranged windings are energizeduntil the magnets have cooled through their Curie temperature to about600-700 C., which ordinarily takes about five to ten minutes at ambienttemperatures.

The permanent magnets to which the invention is particularly directedare those produced from iron-cobaltnickel-aluminum alloys commonly knownas alnico 5. While alnico 5 is the most widely used ferromagneticmaterial in speaker magnets, other permanent magnetic materials mayobviously be used, so long as they are useful in the production ofhigh-energy permanent magnet loudspeakers.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A process of orienting a permanent magnet to form a preferreddirection of magnetization along a curved path disposed about the axisof the magnet having a first pole around a first portion of the sidesurface of the permanent magnet and a second pole around an axiallyspaced second portion of the surface of the magnet comprising raisingsaid permanent magnet to a temperature above its Curie temperature,

completely surrounding said permanent magnet with a magnetic fieldaxially aligned with said permanent magnet and having a north pole atone axial end of said magnet and a south pole at the other axial endthereof,

passing a magnetic field axially through said permanent magnet from oneof said poles to the other of said poles through a curved path disposedabout the axis of said magnet while said magnet is cooled through itsCurie temperature.

2. A process of orienting a plurality of permanent magnets to form apreferred direction of magnetization along a curved path disposed aboutthe axis of each magnet having a first pole around a first portion ofthe side surface of the permanent magnet and a second pole around anaxially spaced second portion of the surface of the magnet comprisingraising said permanent magnets to a temperature above their Curietemperature,

surrounding said permanent magnets with a series of magnetic fieldshaving periodically arranged poles completely surrounding theextremities of the magnets,

thermally insulating said permanent magnets from the sources of saidmagnetic fields,

passing magnetic flux from one of said periodically arranged poles tothe next adjacent pole axially through said permanent magnets while saidpermanent magnets are cooled through their Curie temperature.

References Cited UNITED STATES PATENTS L. DEWAYNE RUTLEDGE, PrimaryExaminer G. K. WHITE, Assistant Examiner US. Cl. X.R.

